Electron guns employed for "probe"-type applications are generally provided with a pointed cathode taking the form of either a sharpened cylinder or the apex of a wire hairpin. The pointed cathode is positioned within a cylindrical aperture of a whenelt cup-shaped electrode. Guns thusly constructed have a disadvantage in that it is difficult to maintain the cathode configuration and the relative positioning of the cathode and grid electrode during operation. In addition, electron guns of the type described are expensive to fabricate because of the cost of configuring the relatively exotic single crystal material, such as lathanum hexaboride, required for the cathode. Further, the possibility of outgassing of the metallic wehnelt cup by back ion bombardment or arcing can result in a destructive discharge to the cathode tip.